For so called liquid system tools, i.e. electrical handheld, portable or transportable power tools that operate with an internal or external liquid system, there are national regulations dictating that the tool should typically be equipped with a residual current device, RCD, or a ground fault circuit interrupter, GFCD (the terms may be used interchangeably in this disclosure) for protection against hazardous ground fault current, in order to be allowed to be sold and marketed.
The liquid system typically functions as a cooler or cleaner for the electrical tool, however if a fault occurs there is a risk that liquid may escape the system and that hazardous currents may be lead by the liquid to the housing of the tool and possibly harm an operator of the tool.
The RCD prevents this from happening by measuring the electric current flowing in the line conductors, or conductor wires, and comparing it to the electric current flowing in the return conductor. If the sum of these currents is not zero, then it is an indication that the current is disappearing somewhere else, typically through the protective earthed housing of the tool and possibly through the operator. When it is detected that the sum of the currents is not zero or not above a threshold value, the RCD is configured to break the power so that no current flows in the tool. The RCD will trig again until the error resulting in the leaking currents and the ground fault has been taken care of.
A typical conventional RCD is installed at the extension cord or power cable of the electrical tool or at the main power entry, and is typically not able to detect errors that occur due to smooth DCs deviating within the tool. In order to also detect that a leaking smooth DC and high frequency (HF) currents are present, an additional RCD for this purpose may be added to the regular RCD for detecting leaking DCs.
However, the typical implementation is expensive, bulky, fragile and not very suitable for handheld of portable tools in construction environments.
Therefore, there is a need for an improved RCD for ground fault protection for liquid system tools.